Rheostat



June 12, 192R P. cRosLEY, JR

RHEOSTAT Filed Oct. 9, 1922 a Patented June 12, 1928.

UNITED STATES 'IPOWEL CROSLEY, JR, OF CINCINNATI, OHIO.

RHEOSTA'I.

Application filed October 9, 1922. Serial No. 593,403.

My invention relates to rheostats, and more particularly to those for use in circuits of low voltage, as in radio receiving sets or any other installation where a large number of relatively small variations of resistance are required,to afi'ord appreciable variations of current with such low voltage.

The object of my invention is to provide a simple, compact, and inexpensive rheostat,

0 easy to install, especially under the conditions encountered in supplying parts of apparatus to various userswho assemble them variously to suit their own wishes. A further object, preferably, is to insure durability of the reheostat both as to the effects of mechanical wear and electrical effects, in-

cluding heating. Other objects will appear,

in the course 0 e ensuing description.

I attain, these objects by the device illustrated, for example, in the accompanying drawing, in which- Figure 1 is a rear or inside elevation of a rheostat embodying my invention, parts of the cabinet or support and of the lead wires or buss-bars being shown in their relation thereto, and the rheostat'being adjusted to include about one-half of its resistance in the circuit;

Fig. 2 is an uprig'ht section on the planes of the broken line 2-2 of Fig. l;

Fig. 3 is a view similar to Fig. 1, showin a modification;

ig., 4 is an upright section on the planes of the broken line 4-4 of Fig; 3.;

Fig. 5 is a detail perspective view of the mounting of Figs. 3 and 4;

Fig. 6 is a fragmentary View showing the connection of the core to the mounting and the way in which the resistance wire is led 'out at this connection;

F i 7 is a partial section similar to Figs. 2 an 4, showing a second modification; and

Fi 8 is a similar view showing a third modiTcation.

In all of the examples, the core 1 is curved into almost a complete circle with its ends almost meeting, thusbeing annular in form. Its cross-section, as shown, is that of a flat rectangle with its lesser dimension radial. to the curving, so that it presents one of its broad flat sides radially inwardly, as the concave side of the curved body. Such a core has an insulating surface; and preferably it is entirely of insulating material. The most desirable material for this core is insulating material that may readily be hard rubber,

ter of the wire,

and outside they the lcore ends are firmly clamped to the cup 'wal bent to the curved or annular form, such as fiber,-or any of the numerous insulating compositions of this character.

The resistance wire 2 preferably is of a metal or alloy having a high specific reslstance to electrical current, a low temperature coefiicient, and resistance to wear and corrosion. Such wire being. readily obtainable on the market, further description thereof herein' will be unnecessary. This wire, or any suitable wire, of the gauge appropriate to afford the desired resistance, has one end part 3 passed through the insulat- 1ng core 1 a material distance from one end of the core, and clinched or otherwise suitably secured, without electrical connection to any other conductor. This wire 2 is wound uniformly, in spaced turns, usually aflittle farther apart than the diame around the core 1, preferably is bent to its curved or anand the opposite end part 4 of the wire 2 is passed through the core 1, from the outer to the inner side, near the opposite end of the core, for electrical connection as will be described. The wire being tightly wound on the core, its turns will partake substantiallyof the rectangular outline of the core cross section, and will be stretched firmly across the inner or concave side of the core at substantially equal intervals, so that by making electrical connection with any one of these turns along this inner side, this turn and all turns between this and the electrically connected end 4 can be included in the circuit.

As shown in the first example, Figs. 1 and 2, the mountin 5 is a shallow cup having an insulating sur ace, and preferably made entirely of insulating material of a rigid nature; as, for example, porcelain or other earthenware, or glass. The core 1, with its wire 2 wound thereon, fits snugly in this cup mounting 5, and. fastening elements or screws (land 7 pass through the wall of the cup and through the end parts of the core 1.

before the core nular form;

Preferably, these screws ass through from the inside, so that their eads are inward;

receive .nuts 8 by which B allowing these screws to pro'ect beyond their nuts 8, their ends may rea y contact with the electrical connectors or buss-bars 9 by which the rheostat is included in the desired circuit.

The'screw 6 passes through the core and p thus forming one terminal of port in which the rheostat, along with other instruments, is. installed. This shaft 10 has on its outer end the knob 13, tightly secured erably,

thereto so that the shaft 10 will turn with the knob in either direction; and also, prefthe knob and shaft carry with them pointer 14 which serves to indicate, at the outside, the setting of the rheostat, which, in practice, is concealed inside the cabinet or behind the panel. 'As here shown, a small vbolt or screw 15 secures the mounting 5 to the panel 11, with stop for the pointer 14, thereby its head outside, just below the knob 13; and this head serves as a stopping the knob and shaft.

rier or guide 16 is from end'to end, axially thereof; its exterior In the example of Figs. land 2, the carcylin'dric'al, with a bore diameter being reduced about midway of its length, forming a shoulder 17. It has a transverse bore through its largerpart, re-

eeiving the inner end part of the shaft 10 snugly; and a small set screw 18 is tapped into the adjacent end of the axial bore, to engage in a depression 19 properly located in the s aft '10 to maintain the correct relative positions'of theguide 16 and the pointer or index 14. Between this guide 16 and the inner face of the mounting 5, a connectorsprin 20 has one end part 21 coiled around the s aft 10,- with a washer 22 between its -vex head 24 lying out free end and the guide 16; the main part of this connector-spring 2O lying against the face of the mounting 5 and extending substantially straight thereacross, out to the cup wall adjacent tothe other fastening element or screw 7 where it isbent up along the .wall', with a loo around and clamped under the head of the screw 7 Thus the other terminal of the rheostat is formed;

The axial bore of plunger or contact element 23 comprises a,

stem sliding in this smoothbore, and a conagainst the aforedescribed inner parts of the turns of the resistance wire 2. A s ring 25 is coiledaround the reduced part. 0 the guide, compressed between the under side of the preferably is'flat,

ring presses the :lly outward for witheach contact element 23 -radifirm contact of its head successive turn of resistance wire this end under its head -this spring 25,

'21 would be more compressed.

the guide 16, from the transverse shaft-receiving 'bore out to the.

head 24, which. and the shoulder .17.

of the connection including the "larger part of the guide 16, the wa'sher22, and the connector-spring 20; and it will be seen that as well as the spring 20, heavy to avoid fusing or the heating effect of the they are of good conducting metal, as brass or bronze, preferably, further avoiding rise of temperature in these springs. The spring 20, by virtue of its part- 21, permits the rheostat to be installed on panels or other supports of various thicknesses yet holds the parts firmly, with the knob 13 back against the face of the-panel or support. Thus, if the panel 11 in Fig. 2 were thicker, the spring'part may be amply annealing from current. Also,

installation on a much thicker panel or support, the shaft depression 19 nearer its. end, iii line with the first depression 19; .thus receiving the set screw 18 and avoiding excessive compression of the spring part 21. However, in

practice, most panels are thin enough to avoid the need of such extra depression 19. Since the contact element 23 may properly contact with the inner parts of the resistance wire.2 anywhere across the inner or concave faceof the core, ing on various thicknesses of panels do not affect the nature of the contact; and any slight axial motion of the shaft 10, permitted by such a spring control, merely allows the contact element 23 to travel in different zones, avoiding concentration of the wear on the wire 2 and thus adding to the the variations due to mount To permit 10 mayhave an additional durability of the rheostat. The cup mounting 5 maintains the core 1 and its wire 2 in close approzn'matidn to a truly circular shape, avoiding much of the radial variation WhlCh the spring 25 compensates for; thus permitting a more even pressure of this spring and accordingly a more uniform contact with the wire 2. Also, it may act as a protector of the core and wire, as well as a protector of adjacent objects from the heat generated in the resistance wire 2; as for instance should the panel 11 be of wood, or other combustible material. Such protection is more desirable,

as to heat the wire excessively; in which case, also, the core should be of insulating material able to withstand this heat.

Howeverf'n the glse of this. rheostat in radio receivin sets, and similar installations, the heating of the wire 2 is not such as to'require these precautions; and the outside rotection against heat isnot heeded. For t 0 core, a fiber or the like, not softened if the voltage is suo by the heat, is preferable to hard rubber or J these con itions Thus, in F igs." 3 to 6, inclusive, the core 1 carriesthe wire 2 with its ends 3 and 4 secured afjn the first example; but the mounting 5 i a flat, relatively wide strip of metal bent with one part 26 at right angles to the other larger part 27 (Fig. 5,) which smaller part 26 has a small opening 28 anda larger opening 29. The smaller opening 28 receives the fastening means or screw 7 for the core end part where the resistance wire 2 is not connected; and the larger opening 29 receives an insulating bushing 30 around the screw or fastening means Q extending therethrough and' fastening the other core end artto the mountin 5 with the other P z: a

end of the wire 2'having a 100;} clamped under the head of this screw 6. he core 1 is thus fastened to the smaller part 26 the mounting 5' with the larger part 27 extending radially inward and having an opening-31 near its end receiving the shaft 10, and a smaller opening 32about midway from this opening to the-smaller part 26, receiving the,bol t or screw 15 that secures the mounting 5' to the sup ort or panel 11, with its head outside and Just below the knob 13 and pointer 14, acting as a stop therefor, as in the first example. Since the mounting 5 is a conductor, from the shaft 10 out to the terminal screw 6, the connector-spring of the previous example is here replaced by a mere coiled spring 21' around the shaft 10, against the face of the conduct-- ing mounting 5, with the washer 22 between it and the contact-element guide mounted on the shaft 10. Thefastening screws 6 and 7 carry the clamping nuts 8, and in addition, the lock nuts 33, clamping the lead wires 9'. However, it will ,be seen that the kind of terminal connectionshown in Figs. 1 and 2 may be used here, or this connection may be used in Figs. 1 and 2,; or any suitable connection may be used in either example.

Also, it will be understood that the guide and contact element and spring ,arrangement, for contacting with the inner parts of the wire 2, as shown in Figs. 1 and 2, may be used whether the cup mounting 5 of that example, or the conducting mounting 5 of the present example, be used. However, I

have taken occasion, in this second example,

and extends from its free end of panels or supports 11 does not vary much,

as previously noted. The screw 18, engaged ineither depression 19 or 19, holds the guide 16 to turn with the shaft 10, in proper position relatively to the pointer 14, as in the previous example. The, contact element 23 comprises the convex head 24', but its stem is larger, to slide in the larger axial bore of the guide 16; and the spring 25' is inside this bore between the inner end of the 'stem and the end of the bore, instead of outside the guide as in Figs. 1 and 2. This spring should be amply large to carry the current; and the larger bearing of the enlarged contact element stem in the guide also may be depended upon ductivity directly from contact element 23' to Washer 22, spring 21 and conducting mounting 5, relieving the spring 25 of some of the current. It also will be under- -stood that this contact, guide and spring combination may be used where the cupshaped mounting of Figs. 1 and 2 is used. In Fig. 7, the guide element16" is similar.

'to that of Figs. 3 and 4, but its axial bore the wire. 2 as the shell slides in the guide bore and encloses the spring 25 compressed between the inside of the shell bottom 24. and the inner end of the guide bore. This af fords an even larger contact between the contact elementand its guide, than in Figs. 3 and 4. Y

'In Fig. 8, the shaft 10' is slotted diametrically, from its inner endan ample distance, and also threaded near its inner end. The guide element 16 comprises a tubular radially outer part, and a flat part 34 fitting snugly in the shaft slot and held therein against the pressure of the spring 21' on the washer 22, by a nut 35 screwed on the shaft and having a diametrical' notch 36 in which the edge of the flat part 34 engages, locking the nut 35 under thepressure of the spring 21. Such a guide element 16" is readily made by flattening part of a tube, allowing the unflattened part to form the tubular part of the guide. Thus, a shoulder 37 will be formed at eachside where the unflattened part is the larger, to bear in'against the shaft 10'; and where the flattened part is wider than the unflattened part, shoulders 38 are 1 formed at opposite sides, facing radially 5 outward. These serve for the abutment of the inner end ofthe spring 25 which surrounds the tubular part with its outer end .against the under side of the head 24. of the contact element 23 having its 10 stem sliding inside the tubular part of the guide 16; in this respect being similar to Figs. 1 small bearing between the contact element and its guide; but permitting the 1 s spring thus outside the guide, to be amply heavy to carry the current without overheating. Since the parts are held by the nut 35, which may be screwed along the shaft and locked at any half-turn, this con- 2 struction, including the spring 21', permits 7 a nicer adjustment to panels or supports ,11 of difierent thicknesses, than in the previous examples. Also the parts are considerably lighter than are permitted by the previous 5 examples, especially as compared with those of Figs. 3 and 4, and Fig. 7.

It will be understood that either contact and guide and spring construction, of Fig; 7 or Fig. 8, may be used with the cup mounting of Figs. '1 and 2, although they are here illustrated as used with the bracket shaped mounting of Figs. 3 to ,6, inclusive, only parts of which are shown in these views. Also, under different conditions, other modifications than any of the numerous examples herein given may occur, and variation in materials may be desirable or necessary, as well as in the shape or number of parts. Therefore, while certain constructional de- 40' tails are deemed preferable in connection and 2, with a relatively,

as new and desire to secure by Letters Patent is;

-In a rheostat, a curved supporting core, resistance wire around saidcor'e, a mounting to loe attached to any one of a number of supports of various thicknesses, electrically conducting fastening meansby which both ends of said core are attached to said mounting, said resistance wire having 'one end electrically connected to one of said fastening elements, a shaft turning in said mounting approximately coaxial with-the curve of said core and extending through the support to which the mountin is attached, a

knob on said shaft on the s1de of said support remote from said mounting, a guide mounted on said shaft to turn therewith, a'spring compressed between said guide and said mounting to hold said knob a ainst the support althou h the thickness of the support varies, sai guide and said spring being electrically conductive and said spring being electrically connected with the other fastening element and with said guide, a contact element guided by-said'guide to move radially outward, an a spring in electrical con nection with said contact element and with said guide, pressing said contact element outin direct contact with successive turns of said wire along the inner or concave s1de of said core, as said shaft is turned.

PowEL'cRosLEY, JR; 

